Known in the art is a fuel injector construction that uses compressed air as the high pressure source for an injection event in a fuel injector, and in which air and fuel is premixed in the injector prior to injection. A typical fuel pump pressurizes the fuel. The air can be pressurized by using a separate compressor powered by the engine. Also, the air can be pressurized by using a charging valve that utilizes the pressure in the engine cylinder during the compression stroke to pressurize the air. In this type of injection system, the compressed air effects the opening of the fuel injector to discharge a fuel/air premixed mixture into the combustion chamber and is used for improved fuel atomization.
The charging valve is more efficient than a separate compressor since it does not need a separate power source to run the compressor. Additionally the charging valve does not need to have a location on the engine to mount the separate compressor. The charging valve takes little energy from the engine to operate since it merely draws a little pressure from the already pressurized engine cylinder. The need, then, exists for a charging valve that will compress and store a sufficient quantity of air to operate an air charged fuel injection system.
U.S. Pat. No. 4,899,714 to Schechter et al. discloses an air charging valve assembly capable of this. This charging valve will work within the forced air injection system to charge the air, without the need to have a separate compressor added to power the system. It has the capability to supply sufficient pressurized air for each injection event without overcharging the system. However, because this air charging valve opens outward into the cylinder, when the cylinder pressure drops during the expansion stroke, this residual pressure has a tendency to pull air with residual fuel from the charging valve back into the cylinder, which is detrimental to the overall engine emissions.
The need then arises for a charging valve that will compress sufficient air for use in the air forced injector each cycle without overcharging the system, by using cylinder compressed air as the charging pressure medium, but will not allow residual fuel to be pulled back into the engine cylinder from the charging valve.